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Do you mean TYPE of guitar (steel or nylon string) or playing position?
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Bob BroadleyApr 19 '14 at 19:02

For a proper scientific experiment, it's best not to use hearsay or others' opinions. You should get actual guitars and mics (even mobile phones would do), and log results.Hence, your resources will be guitars/players/mics.
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TimApr 20 '14 at 9:02

Hi Sally - as has been asked, can you edit your question to describe what you are asking. Both Carl and guitarsean have answers which may be right, but without some clarity in your question it is difficult to know.
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Dr Mayhem♦Apr 20 '14 at 20:01

2 Answers
2

Wait: is your experiment intended to answer this question? What exactly do you need to know?

It might be very helpful to take a highly directional microphone and place it at a set of points on a hemisphere about the guitar's surface (plus a highly repeatable plucking mechanism to ensure the source sound pressure is constant). Alternatively, mount a microphone at one position and rotate the guitar about two axes.

Do you mean position of the picking hand, fret hand note position, or position of the mic relative to the guitar?
A guitar played with a pick will be louder than fingers. Plucked or strummed closer to the bridge will seem louder due to added brightness. A mic placed parallel to the sound hole and as close as possible will be the loudest mic position, but frankly will also sound awful. Acoustic guitars are almost never mic'd straight on to the sound hole. Common mic placements to start with are slightly behind the bridge at a 45 degree angle and aimed at the 12th fret, also at a slight angle (so the mic diaphragm is not parallel to the guitar).